TL;DR: The story is about a monster who goes around killing people from various times, possibly through time travel. The reason the journal entries hop from various times is because they're the journals of multiple people that got killed by the monster. By the way, the original story was called "it shall kill tho". It can be guessed that this is a misspelling of "it shall kill thou", which means "It shall kill you".
January 9th, 1987
Tomorrow I will be adventuring in a nearby cave. I don't know what's in it, but there's only one way to find out. If anyone finds this journal, I probably have died from whatever is in the cave.
-Journal entry of John Terry, missing since 1987.
January 3rd, 1792
I'm finally in a new state. I can't wait until I finish my log cabin!
January 3rd, 1792, journal entry 10
It was a monster! A monster killed my mother! It had giant eyes, long legs, and a heart where its head should be.
-Journal entries of Jackson McCarthy, dead from severe mauling and blood loss.
January 1st, 1733
I saw something in the woods today. I went to go investigate. I heard a scream like nothing I've ever heard before, and it sent massive chills down my spine. Then it jumped at me, and ripped my arm clean off! I managed to escape with 1 arm, and make it to the nearest town. But I don't think I'll make it. Just know that the beast was called the SHINGER...
-Journal entry of Marcus Mathang, dead from blood loss
January 5th, 1700
Today I saw something horrible. The people on board the McCarthy were found dead. I saw something crawling out of the ship. But I'm probably just paranoid. And I have to get to bed, so bye.
-Journal entry of John Doe, missing since he went on a hunting trip
I'm going to die today OH GOD I CAN HEAR IT I SHOUDL SHOOT MYSELF OH GOD TELL LISA I LOVE HER
-Journal entry of Jack Adams, dead from suicide
I have compiled together all of these journal entries. All of these deaths happened in England, and all these men died in their early 40s to late 50s. I might be next. I think I just saw it go around my house. But I'm prepared. I have a gun, and a tape recorder to record what it sounds like, and
-Journal entry of Matthew Toren, found dead on January 24th, 2014, unknown cause